This invention relates to electrostatographic printing machines, and more particularly to a method and apparatus for simultaneously developing and transferring a liquid toner image onto an intermediate transfer member for subsequent conditioning thereon.
A typical electrostatographic printing machine employs a photoconductive member that is sensitized by charging to a substantially uniform potential. The charged portion of the photoconductive member is exposed to the light image of a document. Exposure of the charged photoconductive member selectively dissipates the charge to record an electrostatic latent image. The electrostatic latent image corresponds to the informational areas of the document. The electrostatic latent image recorded on the photoconductive member is developed by contact with a developer material. The developer material can be a dry material comprising carrier granules having adhering toner particles. The latent image attracts the toner particles from the carrier granules to form a toner powder image on the photoconductive surface. The toner powder image is then transferred and permanently fused to a copy sheet.
An electrostatic latent image also may be developed with a liquid developer material. In a liquid development system, the photoconductive surface is contacted with an insulating liquid carrier having dispersed finely divided marking particles. The electrical field associated with the electrostatic latent image attracts the marking particles to the photoconductive surface to form a visible image.
Liquid developing imaging processes utilize a liquid developer typically having about 2 percent by weight of fine solid particulate toner material dispersed in a liquid carrier. The liquid carrier is typically a hydrocarbon. In the developing process, the image is transferred to a receiver which may be an intermediate belt. The image on the photoreceptor contains about 12 weight percent of particulate toner in liquid hydrocarbon carrier. To improve the quality of transfer of developed image to receiver, percent solids in liquid should be increased to about 25 percent by weight. Increase in percent solids may be achieved by removing excess hydrocarbon liquid. However, excess hydrocarbon liquid must be removed in a manner that results in minimum degradation of the toner image.
Prior art liquid ink development systems operate such that the photoconductor surface rotates through the developer bath to make contact with the toner. In these systems, the toner particles are attracted to the latent electrostatic image on the photoconductor surface. The motion of the toner particles in the imagewise electric field is generally called electrophoresis and is well known in the art. However, the liquid carrier also wets the photoconductor surface. It is very difficult to transfer the toner image to paper without either first removing the liquid carrier from the photoconductor surface or using the liquid carrier to enable transfer to the paper and subsequently removing the liquid carrier from the paper. In both cases, the liquid carrier must be removed by processes that must include evaporation of the liquid carrier into the air, which causes airborne pollution.
U.S. Pat. No. 4,707,112, to Hartmann, Nov. 17, 1987, relates to an apparatus for developing an electrostatic latent image. The apparatus includes means for furnishing liquid developer material to the image in a development zone and means for dispersing the particles substantially uniformly in the liquid carrier of the liquid developer material at the entrance to the development zone so as to deflocculate marking particles. The dispersing means may comprise means for generating a pulsed electrical field in the developer material at the entrance to the development zone to induce movement of the marking particles and the liquid carrier. The generating means includes an electrode positioned at the entrance to the development zone and means for applying a pulsed voltage to the electrode to generate a pulsed electrical field in the developer material.